The demand for high speed wireless networking is rapidly increasing. High speed wireless networks are desired for both enterprise and consumer applications. As high speed wireless networks evolve and become more ubiquitous, there is a constant demand for higher throughput and longer range. IEEE 802.11n is a wireless networking standard that addresses these needs. IEEE 802.11n employs multiple-input multiple-output (MIMO) transceiver technology to improve performance. MIMO transceivers allow multiple independent spatial data streams to be transmitted or received simultaneously over the same spectral channel of bandwidth. Within a MIMO transceiver each data stream requires a discrete antenna and its own RF processing chain. In order to achieve low costs, low power consumption and a small form factor, an integrated multi-transceiver approach is desired. A unique feature of IEEE 802.11n is that it allows great flexibility in the number and configuration of the spatial data streams in order to meet various system requirements.
Typical MIMO transceivers include a local oscillator for generating a local oscillator signal which is distributed to transceiver blocks located elsewhere on an integrated circuit chip. In order to reduce the form factor of the MIMO transceiver chip, the transceiver blocks are typically arranged adjacent to or as near as possible to the local oscillator. For example, a 2T×2R MIMO transceiver may include a pair of transceiver blocks symmetrically placed on either side of the local oscillator so that the local oscillator signal may be conveniently provided to both transceiver blocks. MIMO transceivers with a greater number of spatial channels, such as 3T×3R or 4T×4R MIMO transceivers, may have transceiver blocks arranged in a more circular or semi-circular pattern around the local oscillator in order to receive the local oscillator signal directly from the local oscillator.
A problem with the existing design approach is that it is not easily scalable. Significant design changes are required to the chip floor plan if it is desired to add an additional spatial channel or otherwise alter the configuration or capacity of the MIMO transceiver. Additionally, the irregular placement of the transceiver blocks in current MIMO transceiver designs make path matching for the separate spatial channels difficult. What is more, each additional transceiver block requires at least 4 additional pins for interfacing the transmit (Tx) and receive (Rx) signals between the transceiver chip and the baseband circuitry of the WLAN system in which the MIMO transceiver is installed. The additional pins for larger MIMO transceivers further complicate the design requirements of a single chip MIMO transceiver.
A new scalable design approach toward single chip MIMO transceivers is desired. Such a new design approach should allow MIMO transceivers of substantially any size to be produced without significant redesign requirements. Such a design approach should also provide adequate path matching between Tx and Rx signal path and provide adequate separation between Tx ports of the same frequency. An improved MIMO transceiver should also reduce the number of pins required to interface the transceiver with the WLAN baseband circuitry.